The present invention relates to respiratory apparatus and more specifically to nasal masks useful for providing pressurized air or therapeutic gas to a patient suffering from an airflow limitation or other respiratory ailment.
Patients suffering from a variety of medical conditions often require supplementary respiratory support. Depending on the nature and severity of the condition, this respiratory support can range from providing an elevated oxygen concentration cloud to the vicinity of the nose and mouth, to forcing ventilation of the lungs by intubating the trachea. In general, a supply of pressurized air or therapeutic gas is provided by a tube or conduit to a delivery apparatus designed to conform to particular body structure.
One style of delivery apparatus is a mask which provides the gas to a nasal area of the patient. Nasal masks are often employed in the treatment of sleep apnea syndrome, characterized by intermittent upper airway obstruction during sleep. Due to the resulting blood oxygen desaturation and frequent arousals from sleep, persons suffering from this condition are often unable to achieve deep sleep for extended periods and are chronically tired and physically compromised.
Since nasal masks are often worn by persons in unmonitored environments for extended periods, such as in the home during sleep, the nasal mask should be comfortable to wear and conform well to the nasal area, thereby defining a substantially sealed chamber. If the mask is deemed too bulky, too heavy, or to fit poorly, the patient will either not wear the mask, wear the mask improperly, or only wear the mask occasionally when the discomfort associated with the respiratory condition exceeds the discomfort of wearing the mask.
One problem associated with nasal masks relates to the conformance of the mask to the nasal area, which is complexly contoured and differs from patient to patient. Customized masks manufactured to suit particular patients tend to be costly; therefore, masks for general use are typically made in several generic sizes, each size being designed to attempt to accommodate a range of patients. If the mask does not form a good seal around the patient""s nose, leakage can occur, reducing the effectiveness of the treatment. When poorly fitting masks are used with variably regulated air supply systems responsive to patient breathing, such as those developed for treating sleep apnea, mask leakage can induce improper system response, which may exacerbate the patient""s condition. Regulated air supply systems and delivery apparatus for treatment of sleep apnea are disclosed in Patent Cooperation Treaty international application number PCT/US93/05095, published on Dec. 9, 1993, as international publication number WO 93/24169; U.S. patent application Ser. No. 08/184,976 filed Jan. 24, 1994; U.S. Pat. No. 5,199,424; U.S. Pat. No. 5,245,995; U.S. Pat. No. 5,522,382; U.S. patent application Ser. No. 08/741,524 filed Oct. 31, 1996; U.S. Pat. No. 5,645,054; and U.S. Des. Pat. No. D398,987, the disclosures of all of which are herein incorporated by reference.
One method of reducing leakage is to provide a compliant sealing flange or surface around a perimeter of the mask in combination with a strap to bias the mask into sealing engagement with the contour of the nasal area of the patient. Typically, the greater the retention force applied by the strap, the better the seal; however, both the strap and the mask can cause excessive pressure on delicate areas resulting in irritation and patient discomfort.
The retention force required to prevent leakage is also a function of forces and torques induced in the mask. For example, the weight of the conduit supplying air or gas to the mask tends to pull the mask downward, away from the patient""s nasal area, when the patient is sitting. Additionally, any movement of the head from side-to-side or up and down can cause lifting of an edge or sliding of the mask and strap. The more rapid the movement, the more pronounced the effect. Mask slippage and displacement are exacerbated in masks employing large diameter, heavy, or stiff tubes which deliver relatively large volumetric flow rates of air, such as those employed in sleep apnea treatment systems.
For nasal masks used by patients when sleeping, the strap and seal arrangement should also accommodate unconscious or reflexive head and body movements. The discomfort associated with masks which apply too much pressure to the head, neck, or nasal area discourage use of the mask during sleep when it is most needed. As a result, treatment is compromised and the patient is ill served by the apparatus.
Accordingly, there exists a need to overcome the limitations of known designs by providing an improved nasal mask which provides a consistent, reliable nasal area seal while being comfortable to wear. Other desirable features include ease of manufacture and low cost.
The present invention provides a nasal mask which is both comfortable for a user and seals reliably over a user""s nasal area. More particularly, the present invention includes a comfortable soft seal affixed to a flexible shell. This soft seal both promotes a comfortable fit of the nasal mask on a user and a reliable seal between the nasal mask and a user""s facial skin.
The design of nasal masks according to the invention provides solutions to several common problems with conventional designs. For example, the nasal mask""s seal distributes contact pressure, unlike many current masks. Also, the design allows the user to comfortably lie in almost any position and to shift positions, either voluntarily or involuntarily, without disturbing the sealing engagement between the nasal mask and user""s face. Additionally, the design provides for a nasal mask of single size that gives a comfortable fit and a reliable seal for a large segment of the population, in contrast to many current masks which either must be stocked in multiple sizes or which simply do not properly fit on users with faces of certain shapes.
According to one aspect of the invention, a nasal mask includes a flexible shell and a seal. The flexible shell contains an inlet and a malleable element disposed about a periphery of the shell for maintaining the shell in a selectable configuration. The seal is disposed along a perimeter of the shell so as to form a chamber within the shell when the mask is donned by a user.
Certain embodiments of this aspect of the invention may include any or all of the following features. The seal can be a thin bladder filled with a very low durometer silicone gel which is molded in a predetermined configuration. The seal may be bonded to the shell or otherwise maintained in sealing relation with the shell.
Some embodiments of the nasal mask can include a conduit attached to the inlet. The conduit may include an angled portion, a rotary connection, and/or a ball and socket connection. Also, the conduit can have one or more openings in a side wall thereof, to provide venting of flow passing through a lumen formed by the side wall of the conduit.
Additionally, some embodiments of the nasal mask can include a headgear apparatus attached to the mask for retaining the mask on a user. The nasal mask may include a retainer disposed about the inlet and cooperating with the headgear apparatus to retain the mask comfortably and reliably on a user. The headgear apparatus can include at least one connector for attaching the headgear apparatus to the mask, the connector being attached permanently or releaseably to the retainer.
According to another aspect of the invention, a system for treating a respiratory ailment in a recumbent or sleeping user includes a mask as described above in communication with a controlled, breathable gas source via a conduit.
According to still another aspect of the invention, a seal for use with a nasal mask includes a bladder having a first surface manufactured from a film of a certain thickness and a second surface manufactured of a thinner film. The bladder can be filled with a material, such as a silicone gel, having a durometer value of less than about ten on a Shore OOO scale. Additionally, when manufactured, one surface of the bladder can be substantially planar.